In the optical cable telecommunications industry, when optical fibers are connected in series, this may be done either with a mechanical connector or by fusing the ends of the fibers together in a packaged connection splice. In either case, adjacent ends of the in series fibers are held in axial alignment. End portions of optical fibers extending from the packaged splices may be coiled in organizing trays which also house the packaged splices An arrangement of this type is shown in U.S. Pat. No. 4,359,262, granted Nov. 16, 1982 and U.S. Pat. No. 4,489,830 granted Dec. 25, 1984.
In the electrical cable telecommunications industry, conductor wires of an electrical telecommunications cable entering a customer's premises are normally connected to conductor wires of the customer's internal network by the use of a distribution frame. Incoming cable extends to the distribution frame and the jacket and other material surrounding the core of the cable is removed for a distance along the cable from its end to expose the core. Groups of insulated conductor wires are directed from the core and are connected to terminals on the incoming side of different connectors held by the frame, one group to the terminals of each connector. Conductor wires of the internal network are then connected to other terminals on the outgoing side of the connectors so that each connector wire of the internal network is connected to an individual conductor wire of the incoming cable. A typical distribution frame is described in U.S. Pat. No. 4,278,315 granted July 14, 1981 in the name of B. T. Osborne. This arrangement of distribution frame allows for removal and reinsertion of conductors of the internal network or for interchange of terminals for these conductor wires without any need for the customer to interfere with the terminals of the incoming cable.
Thus, an incoming electrical telecommunications cable is connected to the conductor wires of a customer's internal network in an essentially straightforward manner and in a compact arrangement of distribution frame. In such a compact arrangement, as many as five hundred connections are possible to conductor wires of a customer's internal network with a frontal area of a rectangular distribution frame provided by side measurements of approximately 8 inches by 12 inches. However, in the optical cable field, which is more recently being developed, it has not been possible to provide such compact arrangements of distribution frames to connect an incoming cable directly with the optical fibers of an internal network. This is partly because no practical optical cable distribution frame has been designed which gives a high density of connections. It is also partly due to methods of making optical fiber connections which are wasteful of space.
In this latter regard, while optical fibers of the incoming cable could be spliced directly to the fibers of the internal network, this has been shown to be unsatisfactory, because splicing is a substantially permanent connection which hampers the customer's freedom to remove, or interchange connecting positions to the fibers of his internal network. Hence, it is advantageous to be able to use mateable mechanical connectors between the incoming optical cable and the internal network. Mateable mechanical connectors are quickly connectable and disconnectable. With these connectors mounted upon incoming optical fibers (i.e. of the incoming cable) and upon fibers of this internal network this allows for selectively removing and interchanging fibers of an internal network with incoming fibers. However, mechanical connectors require an inordinate amount of time to connect to their respective fibers and for this reason, the use of mechanical connectors to connect incoming optical fibers of an incoming cable directly to fibers of an internal network is commercially unacceptable to cable installation companies.
In order to avoid this problem, incoming optical fibers are conventionally joined to optical fibers of an internal network by use of structures referred to as "pigtails". A pigtail is located in series between a respective incoming optical fiber and an internal network fiber so as to connect them together. A pigtail is a factory made item which comprises a protection surrounded optical fiber of certain length (referred to herein as a "pigtail fiber") and a mechanical connector which is joined to one end of the pigtail fiber. Optical fibers of the incoming cable are connected to the free ends of pigtail fibers by splicing operations, such operations being less time consuming than with the use of mechanical connectors. The splicing operations thus optically couple the optical fibers of the incoming cable with the mechanical connectors of the pigtails. These connectors are mounted upon a framework to make them readily accessible for the customer to connect the optical fibers of his internal network thereto.
While the conventional arrangement described above for connecting incoming optical cables to a customer's internal network has been found to be largely acceptable, design arrangements are unsatisfactory in some respects. In one conventional arrangement, the incoming cable is spliced to the pigtail fibers at a different location from that in which the connectors are mounted upon the framework. No compact and simple connection arrangement is thus produced in one distribution frame. For this reason, the pigtail fibers essentially require surrounding protection. Protection is normally in the form of a surrounding loose tube which allows for lateral freedom of movement of each individual fiber. Suggestions have been made for having a common holder for the splices and the pigtails to allow for ease of access by a customer. However, while these suggestions could eliminate the need for surrounding protection to the pigtail fibers, only a few of these suggestions could provide for ease of access to the cable installation company into the holders in the event of problems occurring in the connections or in the incoming fibers.
In one of these structures, as described in German Offenlegungsschrift 2735106, a housing carries a tray which is pivotally mounted for movement in and out of the housing. Incoming optical fibers are stored within the tray and are connected to pigtail fibers also stored within the tray. The pigtail fibers extend from the tray to pigtail connectors mounted at the rear of the housing. It would be very inconvenient for a maintenance person to service the tray pivoted out from the front of the housing while, at the same time having to concern himself with connectors at the rear of the housing. It would also be extremely difficult to know which of the incoming optical fibers corresponded to a certain connector at the rear of the housing. Apart from this, the width of the housing would need to be such as to provide clearance for pivotal movement of the tray. In U.S. Pat. No. 4,792,203 a structure is described which is similar to that described in the above German document. In the structure described in the U.S. patent, however, the pigtail connectors are all mounted upon trays within a housing. There is a problem that only a small number of pigtail connectors are shown on each tray in the U.S. patent so that only a low density of fiber connections is possible in the housing. In one commercially available construction of this type, the density of connectors is such that only about 250 incoming fibers would be connectable to distribution fibers of an internal network in a housing having frontal area dimensions of approximately 84 inches by 26 inches. The design of each tray is such that an increase in the number of pigtail connections would result in an increase in width of the housing to accommodate the tray.
In addition, in both of the prior arrangements referred to above, the cable installer must install his fibers into each tray with the tray mounted upon the housing thereby cramping the activities of the installer.